Sputtering is one of several well known techniques for applying or depositing a layer on a substrate. Generally, the substrate is placed in a deposition chamber which is evacuated or pressurized to a desired pressure. A particle flux of the coating material is generated within the chamber and the coating or deposition occurs by condensation of the particle flux onto the substrate surface.
In the ion beam bombardment sputtering technique, a high-energy source beam of ions is directed toward the target. The force of the bombarding ions imparts sufficient energy to the atoms of the target to cause the energized atoms to leave the target and form a particle flux. The resulting deposition upon a substrate forms a thin film.
Sputtering targets may be, for example, solid metallic blocks of a selected element or alloy. For sputtering of ceramic materials, targets may be dry powders made into a unitary porous structure. Other dry powder targets may be prepared by mixing the materials to be deposited into a binder-solvent slurry, casting the slurry into a mold, and applying heat to drive off the solvent and cure the binder. Such targets are prone to impurities (from the binder), frequent cracking from thermally-induced stresses, blistering (from embedded gasses), and difficulty in repairing targets damaged during the sputtering operation.
The use of a shield surrounding a target, and which is of the same material as the target, is described in Kokai Publication No. JP 63-83257. In that publication, the entire target shield is of the same material as the target. In one example, where the target material is made of silicon dioxide (SiO2), the entire shield is also made of bulk silicon dioxide, which is neither flexible nor malleable. In another example, where the target material is aluminum, the entire shield is made of aluminum sheet or plate. In another Japanese publication, Kokai Publication No. JP 53-99082, a high-frequency sputtering device is disclosed which is constructed with a shield plate arranged on a support between the base and the target. The surface of the base support and shield plate facing the target are coated with the same material as the target. The publication actually describes such coatings as plates or disks which are held in position by brazing. This implies relatively large masses comprised of the target material. The utility of that invention would be restricted to targets which are solid metals or alloys in that the same material as disclosed is evidently a rigid mass and must also be a suitable candidate for brazing.
U.S. Pat. No. 4,416,755, discloses and claims a sputtering apparatus comprising shield means having a low sputtering efficiency compared to a sputtering target. The shield means are disposed in a vacuum chamber between stray ion beams and the vacuum chamber surface and any implements contained in the chamber so that sputtering of the vacuum chamber surface and/or the implements by a plasma is minimized. Dependent claims in the patent describe the shield as flexible and made of carbon. The patent does admit to some sputtering of the carbon as possible, although at a much reduced level compared to unwanted sputtering of the stainless steel vacuum chamber surfaces.